Fusion marking of metal articles



I April'14, 1970 w. M. SMITH 3,506,801

FUSION MARKING 0F METAL ARTICLES Filed May 23, 1968 INVENTOR. WALTER M.SMITH his ATTOIRNEY United States Patent-O ABSTRACT OF DISCLOSURE" 1 3Claims I A metal article is marked for identification by fusing to itssurface a nugget of a second metal which contrasts with the metal of thearticle. i1

This invention relates to the marking of metal articles foridentification purposes. It is more particularly concerned with fusionmarking a metal article during its processing so as to permit its lateridentification.

In the manufacture of metal articles such as sheets, tubes, rods, shapesand the like, it is frequently desirable to mark the article during itsmanufacture so that the article can be later identified. For example, itis often desirable to mark an article coming out of a heating furnace orfrom a rolling mill so that it can be identified from other likearticles after the articles have been collected, or after they haveundergone further processing. Where successive articles are made from asingle billet, bloom, ingot or other unit of starting material, such amarking serves to identify the beginning or end of the unit of startingmaterial so as to distinguish its product from that of the next unit ofstarting material. Where successive articles are inspected at anintermediate stage of their manufacture it is sometimes more convenientto segregate the marked articles from the unmarked articles at a laterstage of their manufacture or handling.

It is difiicult to mark satisfactorily articles which scale on heating.Surface scale, in subsequent handling of the article, falls offpartially or wholly, carrying with it markings which do not penetratebelow the scale. Markings which indent the surface of the articleprovide notches for stress concentrations which can lead to prematurefailure of the article in service. The problem is particularly acute inthe rolling of-steel into finished products because of the hightemperatures at which steel is processed, but it also exists in themarking of articles of other metals.

It is an object of my invention, therefore, to provide a process ofmarking a metal article so that later it can be positively identified,and to provide articles so marked. It is another object to provide sucha process applicable to articles heated to high temperatures. It isanother object to provide such a process applicable to articles withscaled surfaces. It is another object to provide such a processpermitting automatic identification of the marked articles. It isanother object to provide such a process which is not detrimental to theservice life of the marked article. Other objects will appear in thecourse of the description of my invention which follows.

I have found that a metal article, heated or otherwise, can be providedwith an identifying mark which is later distinguishable by fusing to itssurface a nugget of a contrasting metal. By nugget I mean a small massof a size such that its exposed portion consists of the contrastingmetal. The nugget need not be raised above the steel surface to anyconsiderable extent. By contrasting metal I mean a metal which isvisually distinguishable from the metal of the article, such as bycolor, or which can be readily distinguished because it has a propertydifferent from those of the metal of the article. Visuallydistinguishable metals are copper and steel, for example.

n 3,506,801 Patented e, 1am

ice

Metals distinguishable by their properties are magnetizable andnonmagnetizable metals, foriexample. I prefer to fuse, the nugget to themetal article by bringing the article int'ocontact with an electrode ofthe marking metal and passing an arc welding current, from electrode toarticle. Apparatus suitable for the practice of the presently preferredembodiment of my invention is shown schematically in the attachedfigures, to which 'reference'is' now made. 7

FIGURE 1 is a schematic elevation of apparatus suitablefor the practiceof my invention. FIGURE 2 is a plan of a portion of an article of myinvention so marked. The article 1 to be marked, shown as a length ofpipe, is supported for travel on a conveyor or 'run-out' table,

not shown. If the article is hot or hasbeen heated, its

surface is covered with scale 8. The conveyor or runout table is made ofa conductor so that through it article 1 is electrically connected toground 2. One terminal of a current supply 3 which is conventionally awelding generator is also connected to ground 2. The other terminal 4 ofcurrent supply 3 is connected to electrode material 6 fed from electrodesupply means 5. These means 5 are insulated from ground and are adaptedto feed electrode 6 in the form of a rod or wire toward article 1 as isrequired. Electrode 6 is made of a metal which contrasts with the metalof the article 1 as I have described. Current supply 3 is provided withcontrol means, not shown, to provide pulses of current as they arerequired.

In my process electrode 6 is advanced by electrode supply means 5 intocontact with the surface of article 1. The latter need not be stationarybut can maintain contact with electrode 6 as article 1 moves along itsrunout table. When article 1 is to be marked, a pulse of welding currentis caused to pass through electrode 6 and article 1 from current supply3 to ground 2. That current forms a momentary are between electrode 6and article 1 which fuses a portion of the end of electrode 6 to article1 as a nugget of metal 7. The presence of scale 8 which is relativelynonconducting does not interfere with my process. Current supply 3 isadjusted to provide an are which penetrates scale 8 between'electrode 6and article 1. The nugget 7 of electrode 6 fuses or welds to article 1and to some extent alloys with it. If too hot an arc is struct, all themetal of nugget 7 will alloy with that of article 1, and contrast willbe lost. The are must be adjusted so that at least the surface of nugget7 does not alloy with the metal of article 1. If the arc is not hotenough, it does not penetrate the scale. and the nugget deposited is notwelded to the underlying metal.

The nugget of metal 7 so deposited is visually distinguishable eventhough article 1 undergoes further processing when the metal ofelectrode 6 is of a different color from that of article 1. As I havementioned, a nugget 7 of copper on a steel article 1 distinguishes itfrom other steel articles not so marked. A nugget of aluminum alsodistinguishes a steel article to which it is applied from other steelarticles not so marked although the contrast is not as great as betweensteel and copper.

A nugget of aluminum on a copper article visually distinguishes it fromother copper articles, and conversely a nugget of copper on an aluminumarticle distinguishes it from other aluminum articles. Othercombinations of metals suitable for my invention will suggest themselvesto those skilled in the art.

Articles of nonmagnetizable metal are conveniently marked for automaticdetection by welding thereon a nugget 7 of magnetizable metal such asiron or steel. When the marked articles are to be separated from theunmarked articles, all are moved successively past magnetizing means andthen past a search coil, in which signals are generated by the nuggetsof magnetized metal.

electro to A diameter and a welding current of 40 to 60 amperes withentire satisfaction. The nugget 7 g iii u thevrelatively sriiallamou nt'of ated ltsjffdcposition, nor in anyother way.

pe eslrha wsed momma... 1

passing through the electrode, scale, and the article a 1 weldin urret-v slaptss qandflaslilisted to we d. atnugget of electrode metal to thearticle so that it is not dislodged by further processing withoutalloying the outer surface of the nugget with the metal of the article.

in which the contrast is be- ,1 .UNITE s JOSEPH -V'; TRUHE', Primary*Exarninef W."D. BROOKS;Assistant Examiner"

